function R = covinv(mdl)
%COVINV Gets the inverse of covariance matrix
%
% [ Syntax ]
%   - R = covinv(mdl)
%
% [ History ]
%   - Created by Dahua Lin, on Dec 23, 2007
%

if ~isempty(mdl.invsm)
    R = mdl.invsm;
else
    R = inv(mdl.sigma);
end